U.S. patent number 8,152,245 [Application Number 11/662,482] was granted by the patent office on 2012-04-10 for vehicle system having regenerative brake control.
This patent grant is currently assigned to Kelsey-Hayes Company. Invention is credited to Mark D. Lubbers.
United States Patent |
8,152,245 |
Lubbers |
April 10, 2012 |
Vehicle system having regenerative brake control
Abstract
A method is provided for controlling the braking of a vehicle
that has a first set of friction brakes for applying a first apply
brake force to a first set of wheels and a second set of friction
brakes for applying a second brake apply force to a second set of
wheels. A powertrain assembly is coupled to the second set of
wheels. The powertrain assembly includes a regenerative braking
unit capable of recapturing kinetic energy from the second set of
wheels. The vehicle is braked in a first phase of control using
regenerative braking to brake the second set of wheels to achieve
up to a first value of braking. The vehicle is braked in a second
phase of control using the regenerative braking to maintain braking
of the second set of wheels at the first value of braking force
while selectively applying the first friction brakes to the first
set of wheels up to a second value of braking.
Inventors: |
Lubbers; Mark D. (Ann Arbor,
MI) |
Assignee: |
Kelsey-Hayes Company (Livonia,
MI)
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Family
ID: |
35810151 |
Appl.
No.: |
11/662,482 |
Filed: |
September 9, 2005 |
PCT
Filed: |
September 09, 2005 |
PCT No.: |
PCT/US2005/032231 |
371(c)(1),(2),(4) Date: |
October 04, 2007 |
PCT
Pub. No.: |
WO2006/029353 |
PCT
Pub. Date: |
March 16, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080100129 A1 |
May 1, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60608468 |
Sep 9, 2004 |
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60686802 |
Jun 1, 2005 |
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Current U.S.
Class: |
303/151;
303/152 |
Current CPC
Class: |
B60W
20/13 (20160101); B60W 10/184 (20130101); B60W
10/08 (20130101); B60K 6/48 (20130101); B60T
13/586 (20130101); B60L 7/18 (20130101); Y02T
10/6221 (20130101); Y02T 10/62 (20130101); B60T
2270/602 (20130101); B60W 20/00 (20130101) |
Current International
Class: |
B60T
8/64 (20060101) |
Field of
Search: |
;303/151,152
;180/65.1,65.21,65.31 ;701/22 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Williams; Thomas J
Attorney, Agent or Firm: MacMillan Sobanski & Todd,
LLC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is the U.S. national phase of International
Application No. PCT/US2005/032231, filed Sep. 9, 2005, which claims
priority to U.S. Provisional Application Ser. No. 60/608,468 filed
Sep. 9, 2004, and U.S. Provisional Patent Application Ser. No.
60/686,802 filed Jun. 1, 2005. The disclosures of both applications
are incorporated herein by reference.
Claims
The invention claimed is:
1. A method of controlling the braking of a vehicle that has a
first set of friction brakes for applying a first apply brake force
to a first set of wheels, a second set of friction brakes for
applying a second brake apply force to a second set of wheels, and
a powertrain assembly coupled to said second set of wheels, said
powertrain assembly including a regenerative braking unit capable
of recapturing kinetic energy from said second set of wheels, said
method comprising the steps of: braking said vehicle in a first
phase of control using regenerative braking to brake said second
set of wheels to achieve up to a first value of braking; and
braking said vehicle in a second phase of control using said
regenerative braking to maintain braking of said second set of
wheels at said first value of braking force while selectively
applying said first friction brakes to said first set of wheels up
to a second value of braking with the step of applying said first
friction brakes to said first set of wheels in said second phase of
control exceeding a front bias braking balance control of a desired
brake balance line.
2. The method of claim 1 further comprising the step of braking
said vehicle in a third phase of control by selectively using said
first set of friction brakes to brake said first set of wheels and
using said second set of friction brakes to brake said second set
of wheels together with a desired amount of regenerative braking
when above said second value of braking.
3. The method of claim 2 wherein when braking is applied in said
third phase of control, said friction braking of said first set of
wheels is greater than said friction braking of said second set of
wheels for maintaining front bias balance braking control.
4. The method of claim 2 wherein when braking is applied in said
third phase of control, said braking of said first set of friction
brakes is proportional to said braking of said second set of
friction brakes.
5. The method of claim 2 wherein the amounts of braking applied to
said first set of friction brakes and said second set of friction
brakes are determined as a function of a difference between an
input vehicle braking demand and the actual regenerative braking
applied.
6. The method of claim 2 wherein said first set of wheels are front
wheels of said vehicle and said second set of wheels are rear
wheels of said vehicle.
7. The method of claim 2 wherein said first set of wheels are
coupled to a non-driven axle of said vehicle and said second set of
wheels are coupled to a driven axle of said vehicle.
8. The method of claim 2 wherein, when braking said vehicle during
said third phase of control, said desired amount of regenerative
braking decreases as the amount of braking applied by said second
set of friction brakes increases.
9. A method of controlling the braking of a vehicle that has a
first set of friction brakes for applying a first apply brake force
to a first set of wheels, a second set of friction brakes for
applying a second brake apply force to a second set of wheels, and
a powertrain assembly coupled to said second set of wheels, said
powertrain assembly including a regenerative braking unit capable
of recapturing kinetic energy from said second set of wheels, said
method comprising the steps of: braking said vehicle in a first
phase of control using regenerative braking to brake said second
set of wheels to achieve up to a first value of braking; braking
said vehicle in a second phase of control using said regenerative
braking to maintain braking of said second set of wheels at said
first value of braking force while selectively applying said first
friction brakes to said first set of wheels up to a second value of
braking; and braking said vehicle in a third phase of control by
selectively using said first set of friction brakes to brake said
first set of wheels and using said second set of friction brakes to
brake said second set of wheels together with a desired amount of
regenerative braking when above said second value of braking, when
braking said vehicle in said third phase of control, said desired
amount of regenerative braking is decreased preceding the
application of said second set of friction brakes, said decrease in
the amount of regenerative braking being a function of said amount
of kinetic energy recaptured by an energy storage device of the
regenerative braking unit becoming capacitized.
10. The method of claim 9 wherein no friction brakes are applied
during said first phase of control.
11. The method of claim 9 wherein said first value of braking is a
maximum output of said regenerative braking torque.
12. The method of claim 9 wherein braking from only said first set
of friction brakes and said second set of friction brakes are
applied if a vehicle speed is less than a predetermined
threshold.
13. A method of determining brake control between a non-driven axle
and a driven axle in a braking system where said braking system
includes an electric motor for applying a regenerative braking
force to said driven axle, and where said braking system further
includes a first set of friction brakes for applying a first brake
apply force to a first set of wheels coupled to said non-driven
axle and a second set of friction brakes for applying a second
brake apply force to a second set of wheels coupled to said driven
axle, said method comprising the steps of: receiving a pressure
input command relating to a total braking force for braking a
vehicle; determining an actual regenerative braking force and
comparing said actual regenerative braking force to said total
braking force demand; selecting a brake application strategy as one
of the group of: if said actual regenerative braking force is
greater than said total braking force demand, using said actual
regenerative braking force to brake said driven axle up to said
total braking force demand; and if said actual regenerative braking
force is less than said total braking force demand, determining
said first brake apply force to be applied to said first set of
friction brakes of said non-driven axle and said second brake apply
force to be applied to said second set of friction brakes of said
driven axle, said sum of said first brake apply force and said
second brake apply force being equal to said total braking force
demand with a braking relationship between said first brake apply
force applied to said non-driven axle and said actual regenerative
braking force and second brake apply force applied to said driven
axle that includes a linear portion, then comparing said second
braking brake apply force to said actual regenerative braking force
and selecting a brake application strategy from the subgroup of: if
said actual regenerative braking force is less than said second
brake apply force, then determining a brake apply difference
between said second brake apply force and said actual regenerative
braking force, and then applying said first brake apply force to
said first set of friction brakes of said non-driven axle, and
applying said actual regenerative braking force and said brake
apply difference to said second set of friction brakes of said
driven axle; and if said actual regenerative braking force is
greater than said second brake apply force, then applying said
actual regenerative braking force to said driven axle up to said
second brake apply force and applying said first brake apply force
to said first set of friction brakes of said non-driven axle.
14. The method of claim 13 wherein said actual regenerative braking
force applied to said driven axle is applied up to a first value of
braking force.
15. The method of claim 14 wherein said actual regenerative braking
force applied to said driven axle and said first brake apply force
applied to said first set of friction brakes of said non-driven
axle are cooperatively applied up to a second value of braking
force.
16. The method of claim 15 wherein said actual regenerative braking
force applied to said driven axle, said first brake apply force
applied to said first set of friction brakes of said non-driven
axle, and said brake force difference applied to said second set of
friction brakes of said driven axle are cooperatively applied above
said second value of braking force.
17. The method of claim 16 wherein said actual regenerative braking
force decreases when above said second value of braking.
18. The method of claim 13 wherein braking from only said first set
of friction brakes and said second set of friction brakes is
applied if a vehicle speed is less than a predetermined
threshold.
19. A method of controlling a vehicular regenerative braking system
that includes a first set of friction brakes for applying a first
brake apply force to a first set of wheels coupled to said
non-driven axle, a second set of friction brakes for applying a
second brake apply force to a second set of wheels coupled to a
driven axle, a powertrain assembly coupled to said second set of
wheels, said powertrain assembly including a regenerative braking
unit for applying a regenerative braking force to said driven axle,
said method comprising the steps of: determining a desired brake
balance line representative of a ratio of braking forces between a
first set of brakes of a non-driven axle and a second set of brakes
of a driven axle, said desired brake balance ratio having a first,
a second, and a third control phase; applying said regenerative
braking force to said driven axle in said first control phase up to
a first value of brake force; cooperatively applying said first
brake apply force and said regenerative braking force in said
second control phase up to a second value where said second value
is in a region of front bias braking balance control with said
first brake apply force applied in said second phase of control
exceeding said front bias braking balance control of said desired
brake balance line; and cooperatively applying said second brake
apply force together with said first brake apply force and said
regenerative braking force in a third phase of control up to a
third value of braking.
20. A method of controlling a vehicular regenerative braking system
that includes a first set of friction brakes for applying a first
brake apply force to a first set of wheels coupled to said
non-driven axle, a second set of friction brakes for applying a
second brake apply force to a second set of wheels coupled to a
driven axle, a powertrain assembly coupled to said second set of
wheels, said powertrain assembly including a regenerative braking
unit for applying a regenerative braking force to said driven axle,
said method comprising the steps of: determining a desired brake
balance line representative of a ratio of braking forces between a
first set of brakes of a non-driven axle and a second set of brakes
of a driven axle, said desired brake balance ratio having a first,
a second, and a third control phase; applying said regenerative
braking force to said driven axle in said first control phase up to
a first value of brake force; cooperatively applying only said
first brake apply force and said regenerative braking force in said
second control phase up to a second value wherein said second value
is in a region of front bias braking balance control; and
cooperatively applying said second brake apply force together with
said first brake apply force and said regenerative braking force in
said third phase of control up to a third value of braking with at
least one of said first and said second and third phases of control
including a linear relationship between the braking forces applied
to the first and second sets of wheels, with said third value of
braking disposed in said region of said front bias braking balance
control and with said first and second brake apply force applied in
said third phase of control exceeding said front bias braking
balance control of said desired brake balance line ratio.
21. The method of claim 20 wherein said third value of braking is
disposed on said desired brake balance line.
22. The method of claim 20 wherein said second value of braking is
disposed on said desired brake balance line.
23. The method of claim 20 wherein said regenerative braking force
is not applied if a vehicle speed is less than a predetermined
threshold.
24. A method of controlling the braking of a vehicle that has a
first set of friction brakes for applying a first apply brake force
to a first set of wheels, a second set of friction brakes for
applying a second brake apply force to a second set of wheels, and
a powertrain assembly coupled to said second set of wheels, said
powertrain assembly including a regenerative braking unit capable
of recapturing kinetic energy from said second set of wheels, said
method comprising the steps of: braking said vehicle in a first
phase of control using regenerative braking to brake only said
second set of wheels to achieve up to a first value of braking;
braking said vehicle in a second phase of control using only said
regenerative braking and said first set of friction brakes, wherein
said regenerative braking maintains braking of said second set of
wheels at said first value of braking force while said first set of
friction brakes is selectively applied to said first set of wheels
up to a second value of braking with second phase of control
including a linear relationship between the braking forces applied
to the first and second sets of wheels; and braking said vehicle in
a third phase of control by selectively using said first set of
friction brakes to brake said first set of wheels and using said
second set of friction brakes to brake said second set of wheels
together with a desired amount of regenerative braking when above
said second value of braking with said application of said first
set of friction brakes and said second set of friction brakes
exceeding a front bias braking control of a desired brake balance
ratio during said third phase of control.
Description
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to vehicle braking systems, and
in particular to a method of controlling a braking system having
regenerative brake control.
2. Background of the Invention
Vehicular regenerative braking systems generally capture forward
kinetic energy from braking events and use that recovered energy to
accelerate the vehicle. By using energy recovered from braking, the
energy efficiency of the vehicle is improved. Regenerative braking
may be used on vehicles having hybrid or pure electric powertrain
platforms. On many of these hybrid or pure electric powertrain
vehicle platforms, maximum recovery of braking energy is required
to make the vehicle viable in the market place. Ideally, these
regenerative braking systems are generally transparent (unnoticed)
to the driver.
Vehicles are commonly slowed and stopped with hydraulic brake
systems employing friction wheel brakes. These systems vary in
complexity but a base brake system typically includes a brake
pedal, a tandem master cylinder, fluid conduits arranged in two
similar but separate brake circuits, and wheel brakes in each
circuit. The driver of the vehicle operates a brake pedal which is
connected to the master cylinder. When the brake pedal is
depressed, the master cylinder generates hydraulic forces in both
brake circuits by pressurizing brake fluid. The pressurized fluid
travels through the fluid conduit in both circuits to actuate brake
cylinders at the wheels to slow the vehicle.
Base brake systems in conventionally fueled vehicles typically use
a brake booster that acts during braking to provide additional
force that assists the pedal force created by the driver. The
booster can be vacuum or hydraulically operated. A typical
hydraulic booster senses the movement of the brake pedal and
generates pressurized fluid which is introduced into the master
cylinder. The fluid from the booster assists the pedal force acting
and increases the pressure of the fluid acting on the wheel brakes.
Thus, the pressures generated by the master cylinder are increased.
Hydraulic boosters are commonly located adjacent the master
cylinder piston and use a boost valve to control the pressurized
fluid applied to the booster. Typically the boost valve is
connected with the booster in the master cylinder assembly and
mechanically coupled to the brake pedal for proper operation.
Braking a vehicle in a controlled manner under adverse conditions
requires precise application of the brakes by the driver. Under
these conditions, a driver can easily apply excessive braking
pressure thus causing one or more wheels to lock, resulting in
excessive slippage between the wheel and road surface. Wheel
lock-up leads to loss of directional control and possible greater
stopping distances.
Advances in braking technology have led to the adoption of
Anti-lock Braking Systems (ABS). In ABS, the system monitors wheel
rotational behavior and selectively applies and relieves brake
pressure in the corresponding wheel brakes in order to maintain the
wheel speed within a selected slip range to achieve good braking
force and maintain steering control by avoiding wheel lock-up.
While such systems are typically adapted to control the braking of
each braked wheel of the vehicle, some systems have been developed
for controlling the braking of only a portion of the plurality of
braked wheels.
Electronically controlled ABS valves, including apply valves and
dump valves, are located between the master cylinder and the wheel
brakes. The ABS valves regulate the pressure between the master
cylinder and the wheel brakes during ABS braking. Typically, when
activated, these ABS valves operate in three pressure control
modes: pressure apply, pressure dump and pressure hold. The apply
valves allow pressurized brake fluid into respective ones of the
wheel brakes to increase pressure during the apply mode, and the
dump valves relieve brake fluid from their associated wheel brakes
during the dump mode. Wheel brake pressure is held constant during
the hold mode by closing both the apply valves and the dump
valves.
To achieve maximum braking forces while maintaining vehicle
stability, it is desirable to achieve optimum slip levels at the
wheels of both the front and rear axles. During vehicle
deceleration different braking forces are generally required at the
front and rear axles to reach the desired slip levels. Therefore,
the brake pressures should be proportioned between the front and
rear brakes to achieve the highest braking forces at each axle. In
conventional braking systems of the past, this apportioning was
accomplished by a proportioning valve, which typically proportioned
front and rear brake pressure according to a fixed ratio. Braking
systems may be provided with Dynamic Rear Proportioning (DRP)
systems, which use the ABS valves to separately control the braking
pressures on the front and rear wheels to dynamically achieve
optimum braking performance at the front and rear axles under the
then current conditions.
A further development in braking technology has led to the
introduction of Traction Control (TC) systems. Typically, valves
have been added to existing ABS systems to provide a brake system
which controls wheel speed during acceleration. Excessive torque
applied to wheels during vehicle acceleration leads to wheel
slippage and a loss of traction. An electronic control system
senses this wheel slippage and automatically applies braking
pressure to the wheel cylinders of the slipping wheel to reduce the
slippage and increase the traction available. In order to achieve
optimal vehicle acceleration, pressurized brake fluid (e.g., from
the ABS pump) is made available to the wheel cylinders even if the
master cylinder is not actuated by the driver.
During vehicle motion such as cornering, dynamic forces are
generated which can reduce vehicle stability. A Vehicle Stability
Control (VSC) brake system improves the stability of the vehicle by
counteracting these forces through selective brake actuation. These
forces and other vehicle parameters are detected by sensors which
signal an electronic control unit. The electronic control unit
automatically operates pressure control devices (e.g., pump, boost
valves, apply valves, and dump valves) to regulate the amount of
hydraulic pressure applied to specific individual wheel brakes.
In electric vehicles, in order to extend vehicle range, it is
typical to include some kind of regenerative braking system in the
vehicle. A regenerative braking system seeks to recapture energy
from a moving vehicle by converting kinetic energy to electrical
energy and storing it in an energy storage device such as a
battery. The vehicle is also slowed as a result of the process of
recapturing energy. Most regenerative braking systems work by using
an electromagnetic drive motor(s) as generators. The operation of
one such system is coupled to a selector switch and the accelerator
pedal. When the selector switch is set for regenerative operation,
as the driver removes his foot from the accelerator pedal, the
electric motor is de-energized and coupled to the battery charging
circuit which places an electromagnetic load within the motor. This
simultaneously acts to slow the vehicle as well as generate
electricity that is returned to the batteries.
Regenerative braking systems are cooperatively controlled with the
friction brakes to allow for maximum energy recovery during braking
operations. As the driver applies the brake, brake torque is
generated with frictional braking on the respective wheels and/or
regenerative braking torque on a respective Driven axle. In order
to maximize recovered energy, preference is given to the
regenerative system. The regenerative braking system blends to the
torque generated from the regenerative drivetrain with friction
braking by controlling pressure in the foundation brake system to
achieve a smooth deceleration.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a vehicular regenerative
brake system having an electric powertrain assembly and a friction
brake system controlled in accordance with a preferred embodiment
of the present invention.
FIG. 2 is a schematic representation of the braking operation of
the system of FIG. 1.
FIG. 3 is a graphical representation of a distribution of braking
forces between the front and rear wheels of the vehicle with the
system of FIG. 1.
FIG. 4 is a schematic representation of a control algorithm of the
system of FIG. 1.
FIG. 5 is a schematic representation of a control algorithm for a
sub function illustrated in FIG. 4.
FIG. 6 is a graphical representation of a second embodiment of the
invention illustrating a braking distribution between the front and
rear wheels of the vehicle.
FIG. 7 is a schematic representation of a vehicular regenerative
brake system having an electric powertrain assembly and a friction
brake system controlled in accordance with a third embodiment of
the present invention.
FIG. 8 is a graphical representation of the braking distribution
between the front and rear wheels of the vehicle according to a
fourth embodiment of the present invention.
FIG. 9 is a graphical representation of the braking distribution
between the front and rear wheels of the vehicle according to a
fifth embodiment of the present invention.
FIG. 10 is a graphical representation of the braking distribution
between the front and rear wheels of the vehicle according to a
sixth embodiment of the present invention.
FIG. 11 is a schematic representation of a vehicular regenerative
brake system having an electric powertrain assembly and a friction
brake system controlled in accordance with a seventh embodiment of
the present invention.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a method is provided for
controlling the braking of a vehicle that has a first set of
friction brakes for applying a first apply brake force to a first
set of wheels and a second set of friction brakes for applying a
second brake apply force to a second set of wheels. A powertrain
assembly is coupled to the second set of wheels. The powertrain
assembly includes a regenerative braking unit capable of
recapturing kinetic energy from the second set of wheels. The
vehicle is braked in a first phase of control using regenerative
braking to brake the second set of wheels to achieve up to a first
value of braking. The vehicle is braked in a second phase of
control using the regenerative braking to maintain braking of the
second set of wheels at the first value of braking force while
selectively applying the first friction brakes to the first set of
wheels up to a second value of braking.
DETAILED DESCRIPTION OF THE INVENTION
In the following description of the invention, certain terminology
will be used for the purpose of reference only, and are not
intended to be limiting. Terms such as "upper", "lower", "above",
"below", "rightward", "leftward", "clockwise", and
"counterclockwise" refer to directions in the drawings to which
reference is made. Terms such as "inward" and "outward" refer to
directions toward and away from, respectively, the geometric center
of the component described. Terms such as "front", "rear", "side",
"right-hand", "left-hand", "top", "bottom", "horizontal", and
"vertical" describe the orientation of portions of the component
within a consistent but arbitrary frame of reference which is made
clear by reference to the text and the associated drawings
describing the component under discussion. Such terminology will
include the words specifically mentioned above, derivatives
thereof, and words of similar meaning.
Throughout this specification and claims, the term "in fluid
communication with" refers to a hydraulic connection between two or
more components in which hydraulic pressure is transmittable from
one component to another through a fluid medium. The fluid medium
may or may not contain a valve regulating the flow of fluid between
the components. The components can be in direct fluid
communication, wherein hydraulic fluid can directly flow between
the components. Alternatively, the components can be indirectly in
fluid communication, wherein fluid cannot flow directly between the
components, but fluid pressure is transmittable between the
components. As an example of indirect fluid communication, a fluid
conduit extending between two components may include a movable
piston slidably disposed therein such that the pressure of the
fluid acting on one end of the piston causes the piston to move,
thereby transmitting the pressure to the fluid acting on the other
end of the piston while preventing fluid flow past the piston.
The term "normal boosted braking" refers to the operation of the
described brake systems embodying the present invention, where the
vehicle is on and the brake system has not entered into an ABS, TC,
VSC, or DRP operation.
Pressurized brake fluid produced as a result of action by a master
cylinder is also referred to as a "first pressurized fluid." Fluid
pressurized in a fluid pressure generator circuit other than the
master cylinder is referred to as a "high pressure fluid." High
pressure fluid is metered into a supply conduit for normally
boosted, ABS, TC, VSC, DRP, or regenerative braking operations and
is referred to as a "second pressurized fluid." The terms "first
pressurized fluid," "high pressure fluid," and "second pressurized
fluid" are intended to refer to the same hydraulic fluid at
different pressures in different portions of hydraulic brake
systems during operation of the braking systems. It is to be
understood that the pressure differences between these fluids are
transitory and associated with the operation of the hydraulic
braking system itself.
The brake systems described as embodiments of the present invention
employ many similar components. These similar components are
generally referred to using the same reference numbers.
Referring now to the drawings, there is illustrated in FIG. 1 a
schematic representation of a vehicle system, indicated generally
at 10, which is controlled by a method of the present invention.
The system 10 includes a friction braking system 11a which
typically includes components (described below) to control the
application of hydraulic brake fluid to friction brakes. However,
it is also contemplated that the friction brakes of the friction
braking system 11a may be controlled by any suitable method
including non-hydraulic methods such as electromechanical braking.
The system 10 further includes a regenerative braking system 11b
(described below) which converts kinetic energy of the vehicle into
stored potential energy (typically in the form of electrical energy
stored in the one or more batteries).
The friction braking system 11a includes a pair of frictional front
wheel brakes 12a and 12b for braking front wheels 17 and 18,
respectively, and a pair of frictional rear wheel brakes 13a and
13b for braking rear wheels 20 and 21, respectively. The brakes
12a, 12b and 13a, 13b can be any conventional friction brakes, such
as drum and/or disc brakes and the vehicle system 10 may include a
mix of drum and disc brakes. Each of the vehicle brakes are
independently controlled by a brake module 26 (HCU) and an
electrical control unit (ECU) 27 for controlling the operation of
the HCU 26. The HCU 26 and the ECU 27 will be further described
below.
A first brake circuit 44 is fluidically coupled between the HCU 26
and a front left vehicle brake 12a. A second brake circuit 46 is
fluidically coupled between the brake module 27 and a front right
vehicle brake 12b. A third brake circuit 47 is fluidically coupled
between the HCU 26 and a rear left vehicle brake 13a. A fourth
brake circuit 48 is fluidically coupled between the HCU 26 and a
rear right vehicle brake 13b. Valves within the HCU 26 in
cooperation with a master cylinder 29 are independently actuable
for applying brake fluid to a respective brake circuit. The braking
fluid applied through a respective brake circuit acts on a
respective vehicle brake to apply a braking torque to a respective
wheel for decelerating the vehicle. Wheel speed sensors 30, 32, 34,
and 36, are disposed at each wheel for monitoring the wheel speed
of each respective wheel and providing the sensed wheel speeds to
the ECU 27.
A powertrain assembly 14 includes a rear axle 22 coupled to rear
wheels 20 and 21. The powertrain assembly 14 can be any suitable
system which provides forward acceleration to the vehicle, such as
for example, a hybrid or pure electric powertrain assembly. In the
embodiment shown in FIG. 1, the powertrain assembly 14 is a hybrid
powertrain assembly connected only to the rear axle 22. The rear
axle 22 is thus the driven axle of the vehicle. The hybrid
powertrain assembly includes a combustion engine 15 connected to a
driveshaft 39 which is coupled to a rear axle 22 via a transaxle 16
for providing output torque to the rear axle 22. The hybrid system
also includes an electric motor 19 coupled to the driveshaft 39 for
powering the wheels by an electrical means when the power output
from the engine 15 is disengaged. It should be understood that the
method of controlling the system 10 in accordance with the present
invention can be used with any type of powertrain assembly, whether
the powertrain assembly 14 is connected to the rear axle 22, front
axle 23, both axles, use of a single electric motor or multiple
electric motors each operable for driving a respective wheel.
The electric motor 19 is connected to an energy storage device 24,
such as a battery. The electric motor 19 can provide forward
acceleration of the vehicle via power supplied from the stored
electrical energy of the energy storage device 24. The electric
motor 19 of the powertrain assembly 14 preferably forms the
regenerative braking system 11b and thus functions as a generator
for providing regenerative braking when the powertrain assembly 14
is operated in a regenerative braking mode in which kinetic energy
is captured from the rotation of the rear axle 22 and used to
generate electrical energy which is stored within the energy
storage device 24 for later use. The powertrain assembly 14 is
preferably coupled to a selector switch (not shown) and the
accelerator pedal 25. When the selector switch is set for
regenerative operation and as the driver removes his foot from the
accelerator pedal 25, the electric motor 19 ceases operation as an
output drive device and is coupled to a battery charging circuit
which induces an electromagnetic field in the electrical motor 19
causing the motor to function as an generator generating electrical
energy. The motor 19 (when operating as a generator) is thus driven
by the driveshaft 39 and acts as a load on the driveshaft 39. This
simultaneously acts to slow the vehicle as well as generate
electricity that is returned to the energy storage device 24.
Alternatively, a respective electrical motor (not shown) and a
respective generator (not shown) may be coupled to the powertrain
assembly 14 separately as opposed to utilizing an integrated
electric motor/generator.
The HCU 26 is a unit containing the hydraulic components that are
utilized to control the operation of the vehicle system 10, such as
various valves and hydraulic pumps. The ECU 27 contains electrical
components operatively connected to components of the HCU 26, such
as solenoid coils for operating valves in the HCU 26, and electric
motors for driving the pumps (not shown) of the HCU 26, as well as
other components of the vehicle system 10 to control braking of the
vehicle. The ECU 27 may be integrated with the HCU 26 or may be
remotely located from the HCU 26. The ECU 27 may be any kind of
microprocessor device or string of microprocessor devices (i.e.,
components linked by a vehicular local area network such as a CAN
bus). The ECU 27 is also operatively connected to a variety of
vehicular sensors. The variety of sensors operatively connected to
the ECU 27 typically may include a brake pedal pressure sensor 38
coupled to a brake pedal 28, one or more wheel speed sensors 30,
32, 34, and 36, a battery temperature sensor 40, a state of charge
sensor 42, and an ambient temperature sensor 45. These sensors
provide operational inputs to the ECU 27 that are preferably
evaluated in real-time in order to cooperatively control the
operation of the regenerative braking system 11b and the hydraulic
braking system 11a.
FIG. 2 is a schematic representation of the overall braking of the
vehicle which is accomplished by controlling the front and rear
wheel friction brakes via the friction braking system and
controlling the powertrain assembly to produce braking via the
regenerative braking system. A driver attempting to slow the
vehicle enters a driver input demand 101 by the use of a brake
pedal (shown in FIG. 1). Braking demand may also be developed from
automated input 102 to the ECU such as TC, Autonomous Cruise
Control (ACC), or radar collision avoidance systems or as a
modification of the drivers demand such as occurs during ABS
braking or VSC operation. The driver demand is sensed by the ECU
27.
In regenerative braking system, braking is controlled cooperatively
by the ECU 27 and the PCM 49. The ECU 27 controls the frictional
braking while the PCM 49 controls the regenerative braking. When
the braking demand is received by the ECU 27, the ECU 27 and the
PCM 49 cooperatively communicate with each other to blend the
regenerative braking and frictional braking in accordance to a
predetermined brake blending and balance algorithm 103. Based on
the predetermined braking algorithm, braking controls are executed
for regenerative braking 104 via the powertrain assembly and
friction braking 105 via the friction brakes. Braking demand modes
may include regenerative braking only, friction braking only, or a
combination of both friction and regenerative braking. Since
braking demands of the driver may be greater than that which
regenerative braking may be able to supply, the available
regenerative braking torque is constantly feedback to the brake
algorithm 106. The actual regenerative braking torque is provided
by the PCM to the ECU for determining what additional frictional
braking would be required to decelerate the vehicle when the
braking demand of the driver is greater than the braking torque of
which the regenerative braking system can provide.
Depending on the braking blending and balance algorithm, the brake
system will apply the regenerative braking and friction braking
either independently or in combination with one another 107. If
braking is applied in combination, both friction and regenerative
braking operations are controlled so the operation of the
regenerative braking and the friction braking are unnoticeable to
the driver of the vehicle. The output of the combined braking
operation will be substantially equal to the drivers braking demand
which results in the intended vehicle deceleration as demanded by
the driver of the vehicle. It is also preferred that the balance of
torque between the front and rear axles be controlled by the ECU
108.
To maximize energy recovery, the vehicle system 10 should have
sufficient bandwidth and limited time delay to develop braking
force when requested by the driver. Sufficient bandwidth to
maximize energy recovery provides for good pedal feel and smooth
deceleration.
Vehicles having only one driven axle, such as the vehicle system 10
shown in FIG. 1, should be controlled during braking and
regenerative braking to provide sufficient balance between the
front axle 23 and the rear axle 22. There is illustrated in FIG. 3
a first embodiment of an ideal brake balance between the front axle
23 and rear axle 22, indicated by a broken line plot 50. Note that
the ideal brake balance curve 50 is for a two axle vehicle that
incorporates only a friction braking system. It is also noted that
the ideal brake balance 50, is not linear but slightly curved
biased towards a frontal braking. This is preferred since a greater
braking force on the front wheel brakes 12a and 12b are preferred
than on the rear wheel brakes 13a and 13b due to the load shift
toward the front wheels during deceleration. The desired brake
balance line, generally shown at 53, is the determined is linear
brake balance between the rear and front friction brakes that is
front biased and in spaced relation to the ideal brake balance
curve.
There is also illustrated in FIG. 3 a graphical representation of a
preferred brake blending balance, indicated by the solid line plot
52. The preferred brake balance is accomplished by the method of
the present invention, as described below. To maximize energy
recovery, braking is initially performed only on the driven axle
(i.e., rear axle 22 in reference to FIG. 1) up to a maximum
capability of the regenerative braking system 11b as set forth by
the PCM 49. There is illustrated in FIG. 3 a graphical
representation of the preferred braking distribution, in accordance
with the present invention, between the front wheel brakes 12a and
12b and rear wheel brakes 13 and 13b. It is noted that while the
axes of the graph are termed in units of g's of deceleration,
braking forces by friction braking as well as regenerative braking
as applied, is proportional and equivalent to the deceleration, and
as a result, braking forces and braking values may be utilized
hereafter to describe the functionality of the braking operations
of this graph and alternative embodiments.
To provide maximum energy recovery, generally only the regenerative
braking system 11b is actuated to provide braking for the vehicle
during relatively low deceleration, as indicated by phase I in FIG.
3. This is illustrated graphically as a vertical line indicating
that only the deceleration of the vehicle is produced by the
resistive torque generated by the electric motor 19 acting on to
the driveshaft 39 which is coupled to on the rear axle 22. In this
example, the maximum braking capability of the regenerative braking
system 11b is about 0.2 g at a point A as shown in FIG. 3. During
braking in phase I, the friction braking system 11a, that is, the
friction wheel brakes 12a, 12b and 13a, 13b, are preferably not
actuated. However, it is noted that to utilize regenerative
braking, vehicle speed must be above a predetermined threshold
(e.g., 5 mph). If less than the predetermined threshold, then
vehicle friction braking will be provided by the balanced braking
of the front set and rear set of friction brakes.
When the maximum regenerative torque of the regenerative braking
system 11b is reached, as indicated by point A (i.e., first value
of braking) of FIG. 3, and the driver desires additional braking,
the ECU 27 actuates friction braking system 11a, and more
specifically actuates friction braking on the opposite axle, i.e.,
the front wheel brakes 12a and 12b to provide balancing of the
system 10. This is represented by a horizontal line in the Phase II
of FIG. 3. The braking force of the wheel brake 13a and 13b is
applied until the overall braking torque meets a desired balance,
as indicated by point B (i.e., second value of braking) and within
the phase II, as shown in FIG. 3. During the period of hydraulic
braking and regenerative braking in phase II, the ECU 27 preferably
does not actuate the rear wheel brakes 13a and 13b.
If a higher braking force is demanded by the driver's input, such
as that shown in phase III of FIG. 3, the front wheel brakes 12a,
12b and the rear wheel brakes 13a, 13b, as well as the regenerative
mode of the powertrain assembly 14 (that is, the friction braking
system 11a and the regenerative braking system 11b) are actuated
and increased as necessary to maintain the desired balance between
the front and rear axles of the vehicle until the vehicle fully
decelerates to the drivers braking demand (i.e., third value of
braking of braking). The combined regenerative braking and
frictional braking apply a combined braking force, in phase III, in
which braking forces of the front wheels and said rear wheels are
proportional such that a ratio line defined by a ratio of braking
forces between the front wheels and the rear wheels define a plot
line that is substantially equal to a ratio line defining a desired
brake balance 53. During the brake apply in phase III, regenerative
braking may gradually decrease if the regenerative braking force
can no longer assist the friction braking. This may be the result
of the energy storage device becoming capacitized where no
additional energy can be stored.
There is illustrated in FIG. 4, a preferred control algorithm,
indicated generally at 51, for performing the brake balance
distribution as shown in FIG. 3. The algorithm generally has two
inputs: P.sub.cmd 72, and Act_Torq 73. The input P.sub.cmd 72 is
the hydraulic brake fluid pressure that would be required to
operate the friction brakes 12a, 12b and/or 13a, 13b if no
regenerative braking was available. The value of this input can be
determined by another algorithm (not described herein) that
calculates the driver's desire for overall braking. The input
Act_Torq 73 is the actual braking torque that is applied by the
regenerative braking system 11b as a result of a regenerative brake
torque request.
The algorithm of FIG. 4 includes output Friction_Press 75. The
output Friction_Press 75 is the pressure required in each of the
four wheel brakes 12a, 12b and 13a, 13b which will be necessary to
meet the driver's demand for braking beyond that supplied by the
regenerative braking system. The algorithm further includes two sub
functions: Front_Rear_bal 76 (shown in FIG. 5) and Press_Torq
77.
When the braking demand of the driver is input (i.e., P.sub.cmd
72), the P.sub.cmd input is provided to the Front_Rear_bal 76. The
sub function Front_Rear_bal 76 determines the total torque
equivalent of the P.sub.cmd input as well as the ideal or desired
balance torque required for each of the driven and non-driven axles
of the vehicle. These torques are based on a brake balance
relationship that can be determined from vehicle parameters and
customer design requirements. The algorithm of FIG. 4 generates one
of three different braking strategies depending on the braking
demands of the driver. The three braking strategies include
regenerative braking only, regenerative braking and friction
braking of the vehicle brakes of the only the non-driven axle, and
regenerative braking and friction braking of the friction brakes of
the non-driven and driven axle.
The determination for using the first braking strategy where only
regenerative braking is utilized is described as follows. An
Act_Torq 73 is provided by the PCM 49 to the control algorithm 51
and is the regenerative braking force that is to be applied by the
powertrain assembly 14 for vehicle deceleration. The Driven_Axle 82
and the Act_Torq 73 are summed at summation block 90. (Braking
signals are typically negative, however, for descriptions purposes
all brake apply signals will be discussed herein are in absolute
values. The summation blocks are appropriately marked to input a
positive or negative value for summing purposes.) If the sum is
negative, switch 80 is actuated to operatively connect output of
gate 84 to the Press_Torq 77. Thereafter, the Act_Torq 73 and Total
81 are summed at summation block 91. If the Act_Torq 73 and Total
output 81 are equal, then their sum is zero which results in a zero
value input to the sub function Press_Torq 77 and a zero value
output from the Friction_Press 75. The result is no friction
braking contributed by both the non-driven axle and the driven axle
since the regenerative braking system can independently meet the
braking demands of the driver.
If the summation at block 91 indicated that the Act_Torq 73 is less
than the Total 81, (i.e., positive sum) then the regenerative
braking system has insufficient capacity to meet the entire braking
demands that is required by the driver's input and either the
friction braking of the non-driven axle or the friction braking of
both the non-driven and driven axle must be used in cooperation
with regenerative braking.
A determination is then made whether the friction braking of only
the non-driven axle should be applied or both the non-driven and
driven axle should be applied in cooperation with the regenerative
braking torque. As discussed earlier, the sub function
Front_Rear_bal 76 determines the friction brake balance required to
meet the driver's braking demands (i.e., without regenerative
braking). The Driven_Axle 82 output of the Front_Rear_bal 76 is
summed with the Act_Torq 73 at summation block 90. If the result is
negative (i.e., Act_Torq 73 is greater than that which is demanded
by the Driven_Axle 82), then the driven axle does not require any
braking and the driver's braking demand can be satisfied by the
regenerative braking system and the friction braking of only the
non-driven axle. Switch 80 is actuated to operatively connect gate
84 to sub function Press_Torq 77.
A further determination is made to determine the amount of friction
braking torque required by the non-driven axle. The Act_Torq 73 is
summed with the Total 81 (i.e., total braking demand by the driver)
at summation block 91. The result is the amount of braking force
that is required to be supplied by the non-driven axle. This is the
amount of braking force that is required of the non-driven axle, in
addition to the regenerative braking force, to meet the braking
demands of the driver.
The determination for using the third braking strategy where
regenerative braking and friction braking of both the non-driven
axle and the driven axle are utilized is described as follows. If
the summation at block 90, between the Act_Torq 73 and the
Driven_Axle 82, is positive (i.e., the driven axle braking demand
is greater than the actual regenerative braking torque), then this
indicates that there is insufficient regenerative braking torque to
provide a braking force by the regenerative braking system that
would meet the requirements that are demanded by the driven axle,
in addition to the braking requirements of the non-driven axle.
Switch 80 is actuated to operatively connect gate 85 to the sub
function Press_Torq 77. The difference between the Act_Torq 73 and
the Driven_Axle 82 represents the amount of braking force that is
to be applied by the friction brakes of the driven axle. The
friction braking requirements of the friction brakes of the
Non_Driven Axle 83 as determined by the Front_Rear_bal 76 in
addition to the difference as determined above for the Driven_Axle
82 are communicated to the sub function Press_Torq 77 via gate 85
so that the friction braking from both the non-driven axle and the
driven axle are utilized, in addition to the regenerative
braking.
The sub function Press_Torq 77 converts the friction torque request
to a pressure command as represented by Friction_Press 75.
The following formulas summarize the determination of the
Friction_Press signal:
If the magnitude of the Act_Torq is greater than the demand of the
axle torque:
.times..times..times..times..times..times..gtoreq..times..times..times..t-
imes..times..times.<.times..times..times..times..times..times..times..t-
imes. ##EQU00001## If the magnitude of the Act_Torq is less than or
equal to that of the desired Driven_Axle torque: Non-driven wheel
Friction_press=desired non-driven_axle torque Driven wheel Friction
press=desired driven_axle torque-Act_Torq
There is also illustrated in FIG. 6 a second preferred embodiment
of the present invention. FIG. 6 illustrates a graphical
representation of an alternate brake blending balance plot,
indicated by the solid line plot 54. This graphical representation
is similar to that shown and described with respect to FIG. 3
above. One of the differences is that phase II of FIG. 6 is
enlarged, thereby shifting point B so that rear friction braking
will be actuated and added to the front friction braking at a later
value compared to the braking distribution of FIG. 3. As shown in
FIG. 3, point B is generally lies along the linear slope of the
desired brake balance 53 (for brake systems not having regenerative
braking), which would generally extend through the zero axis.
Comparatively, as shown in FIG. 6, the front friction only brake
distribution extends farther beyond the linear slope of the desired
brake balance 53, thereby increasing phase II. In certain
circumstances it may be desirable to control a brake system as
shown in FIG. 3 since it is closer to an ideal brake balance 50.
However, since the combination of front and rear friction brake
blending in FIG. 3 is performed at a lower braking force in
comparison to that of FIG. 6, the pressure balance and operation of
the front and rear brake circuits should be relatively smooth and
controllable, since more braking is commonly used in lower braking
forces. To accomplish this, it may be necessary for the brake
system to use relatively expensive proportional valves and pressure
transducers. For economical reasons, it may therefore be desirable
to control a brake system as shown in FIG. 6 with a simpler brake
circuit utilizing less expensive valves. Since front and rear brake
blending only occurs at relatively high braking forces and
relatively infrequent, it may not be necessary to provide such as
smooth and controllable brake system.
The control braking strategy as shown in FIG. 6 is ideally suited
for a rear wheel drive vehicle having a simple valve configuration.
In order to blend rear friction braking with regenerative and front
friction braking, it has been known to use methods which require
accurate rear axle pressure control. These methods control braking
in such a way that the front to rear brake balance is maintained
appropriately. For brake blending using rear pressure control a
simple hydraulic circuit can be used that is the same or similar to
a standard Anti-Lock Braking System (ABS) circuit. This is done by
isolating pressure to the rear wheels at a relatively low or zero
pressure during a brake apply, such that the friction and
regenerative brake blending is done mainly with front friction
braking. Rear friction braking is preferably only done at higher
deceleration levels, when the maximum braking capability of the
vehicle is needed.
The benefit of this method is that the rear friction braking does
not need to be as accurate or as smooth as it otherwise would need
to be. The driver is more aware of brake smoothness and accuracy at
lower deceleration levels, when rear friction braking is limited or
zero. Rear pressure blending which is not attempted at these low
deceleration levels does not result in poor braking control. At
higher deceleration levels, the driver does not need or notice as
easily that the rear braking is not controlled as accurately.
At deceleration levels below that which cause the rear friction
braking to be increased, the brake balance is increasingly front
biased as front braking is increased relative to the rear
regenerative braking. This is considered a safe, stable braking
situation.
FIG. 6 illustrates this brake balance strategy. In a first phase of
control, indicated as phase I, regenerative braking is initially
applied to the rear wheels, preferably without any friction braking
to point A. In a second phase of control, indicated as phase II,
for decelerations higher than the regenerative braking alone can
apply, front friction braking is then applied to the front wheels
up to point B, while maintaining regenerative braking of the rear
wheels constant. In a third phase of control, indicated as phase
III, for decelerations above point B (up to the point of the
maximum braking capability of the vehicle, i.e., third value) rear
friction braking is then applied. The combined regenerative braking
and frictional braking apply a combined braking force, in phase
III, in which braking forces of the front wheels and said rear
wheels are proportional such that a ratio line defined by a ratio
of braking forces between the front wheels and the rear wheels
defines a plot line that nears a ratio line defining a desired
brake balance 53 as the combined vehicle braking approaches the
maximum capability braking of the vehicle. Preferably, the front
friction braking is applied is greater than the rear friction
braking so that a front bias braking balance control is
maintained.
In the third phase of control (phase III), the blending of front
and rear friction braking may also include the reduction, or
phasing out, of rear regenerative braking at higher decelerations,
for example for stability control of the vehicle. This reduction in
rear regenerative braking may coincide with or precede the
application of rear friction braking.
The hydraulic circuit used to control pressure could be the same as
is found in state of the art ABS applications, or modified versions
of those such as changes made to make the valves operate in a more
proportional manner.
One of the advantages of this method over conventionally known
systems is that the rear pressure control by the ECU 27 could be
performed using rear wheel slip information as is found in
conventional ABS applications.
FIG. 7 illustrates schematic representation of a vehicular
regenerative brake system having a hybrid electric powertrain
assembly and a friction brake system according to a third preferred
embodiment of the present invention. The vehicle system is a front
wheel drive system utilizing a combustion engine 15 and an
integrated motor/generator 19 for powering the movement of the
vehicle. The engine 15 and the integrated motor/generator 19 are
each connected to the driveshaft 39 which is coupled to the front
axle 23 via the transaxle 16. As discussed earlier, the integrated
motor/generator 19 may include a separate electric motor and
separate generator that cooperatively provide an output torque for
driving the front vehicle wheels 17 and 18, providing an
electromagnetic force for regenerative braking the front vehicle
wheels 17 and 18, and for recapturing energy to be stored in the
energy storage device 24.
FIG. 8 is a graphical representation of the braking distribution
between the front and rear wheels of the vehicle for a front wheel
drive vehicle utilizing regenerative braking as indicated by the
portion of the solid line plot 56. As discussed earlier, only
regenerative braking (no frictional braking) is performed during
low deceleration demands (when above a speed at which regenerative
braking is available). This is indicated by phase I of FIG. 8.
Regenerative braking is performed on the front driven axle of the
front wheel drive system. The regenerative braking portion is shown
by the solid line plot 57 in FIG. 8 and is maximized at 0.3 g at a
point A. Any additional braking demands as demanded by the driver
input requires additional braking assistance from frictional
braking of the rear vehicle brakes 13a and 13b. This is represented
by the vertical increasing braking force, as shown in phase II by
the portion of the solid line plot 58, which extends along the
vertical axis to 0.2 g at point B. During the brake apply of the
rear vehicle brakes 13a and 13b, regenerative braking is still
being applied and energy is being recaptured from the integrated
electric motor/generator and stored in the energy storage device 24
as illustrated in phase II. If higher braking demands are required,
then a brake blending balance between the rear vehicle brakes 13a,
13b and the front vehicle brakes 12a, 12b is provided and is shown
by the solid line plot 59 in phase III. At point B, brake balance
between vehicle brakes 12a, 12b and 13a, 13b follows the desired
braking balance, as indicated by the broken line at 53.
Applying a braking force to a front wheel drive vehicle provides
greater vehicle stability control with respect to yawing of the
vehicle than if braking force were applied to a rear wheel drive
vehicle. For example, applying a high braking force on a respective
road surface condition for a rear wheel drive vehicle may result in
yawing of the rear portion of the vehicle.
Applying the same braking force to a front wheel drive vehicle will
lessen or eliminate vehicle yawing. As a result, it is not required
that frictional braking be applied solely to a respective axle
prior to brake blending both the front and rear vehicle brakes.
Referring now to FIG. 9, vehicle brake blending balance is
indicated generally by the solid black line plot 60. Regenerative
braking is applied to the front axle of a vehicle without any
frictional braking as indicated by the portion of the solid black
line plot 61 in phase I. After regenerative brake apply has peaked
and can no longer apply an increased regenerative braking force on
the front axle, an additive braking force is applied by both the
front vehicle brakes 12a, 12b and rear vehicle brakes 13a, 13b. The
regenerative braking system and the frictional braking system apply
a combined braking force such that a ratio of front axle and rear
axle braking forces nears the desired braking balance 60. This is
indicated by the portion of the solid black line plot 62 of phase
II.
FIG. 10 illustrates yet another preferred embodiment of a braking
strategy for a front wheel drive vehicle. Similar to the
regenerative braking as shown in FIG. 9, vehicle brake blending
balance is shown generally by the black line plot 63. The
regenerative braking applied less frictional braking is indicated
in phase I from 0 to 0.3 g at point A as illustrated by solid line
plot 64. At point A, if higher braking demands are required by the
driver, then frictional braking of both the front vehicle wheels
12a, 12b and rear vehicle wheels 13a, 13b are applied. The combined
regenerative braking and frictional braking apply a combined
braking force in which braking forces of the front wheels and said
rear wheels are proportional such that a ratio line defined by a
ratio of braking forces between the front wheels and the rear
wheels defines a plot line that is parallel to a ratio line
defining a desired brake balance 53. The combined braking force is
shown generally by the portion of the black line plot 65 in phase
II. Similar, to the braking strategy of FIG. 9, the individual axle
friction brake applied prior to the combined frictional brake apply
is not required for the front wheel drive vehicle system.
FIG. 11 illustrates yet another preferred embodiment of the present
invention illustrating a pure electric drive vehicle system. The
vehicle system, as shown in FIG. 11, utilizes a plurality of
electric motors to drive the vehicle system without the use of an
engine as shown in earlier embodiments. The vehicle system includes
a first electric motor 31 coupled to the front axle 23 for driving
the front left wheel 30 when energized. When the first electric
motor 31 is denergized from driving the front left wheel 17, the
first electric motor 31 may perform like a generator for placing an
electromagnetic load the left side portion of the front axle 23 for
performing a regenerative braking operation on the front left wheel
17. Similarly, a second electric motor 33 is coupled to a right
side portion of the front axle 23 for driving the front right wheel
21 when energized. When the second electric motor 33 is denergized
from driving the front right wheel 18, the second electric motor 33
may perform like a generator for placing an electromagnetic load on
the right side portion of the front axle 23 for performing a
regenerative braking operation on the front right wheel 18. Braking
strategies for combined regenerative braking and friction braking
may be applied as discussed earlier for front wheel drive
system.
In other preferred embodiments, a single electric motor may be
utilized on the driveshaft of the vehicle as opposed to utilizing
two electric motors for driving each driveable wheel and
recapturing energy from each driveable wheel. In addition, the pure
electric vehicle as described using a single or dual electric motor
may be utilized on a rear wheel drive system.
In summary this invention includes a method for controlling the
braking of a vehicle that has a first set of friction brakes for
applying a first apply brake force to a first set of wheels and a
second set of friction brakes for applying a second brake apply
force to a second set of wheels. A powertrain assembly is coupled
to the second set of wheels. The powertrain assembly includes a
regenerative braking unit capable of recapturing kinetic energy
from the second set of wheels. The vehicle is braked vehicle in a
first phase of control using regenerative braking to brake the
second set of wheels to achieve up to a first value of braking. The
vehicle is braked in a second phase of control using the
regenerative braking to maintain braking of the second set of
wheels at the first value of braking force while selectively
applying the first friction brakes to the first set of wheels up to
a second value of braking.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle in a third
phase of control by selectively using the first set of friction
brakes to brake the first set of wheels and using the second set of
friction brakes to brake the second set of wheels together with a
desired amount of regenerative braking when above the second value
of braking.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where when
braking is applied in the third phase of control, the friction
braking of the first set of wheels is greater the friction braking
of the second set of wheels.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where when
braking is applied in the third phase of control, the braking of
the first set of friction brakes is proportional to the braking of
the second set of friction brakes.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle an amount of
braking applied to the first set of friction brakes and the second
set of friction brakes is determined as a function of a difference
between an input vehicle braking demand and the actual regenerative
braking applied.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle the step of
braking the vehicle in the second phase of control further includes
selectively applying the second set of friction brakes together
with the first set of friction brakes up to the second value of
braking.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where the first
set of wheels are front wheels of the vehicle and the second set of
wheels are rear wheels of the vehicle.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where the first
set of wheels are coupled to a non-driven axle of the vehicle and
the second set of wheels are coupled to a driven axle of the
vehicle.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where when
braking the vehicle in the third phase of control, the desired
amount of regenerative braking decreases as an amount of braking
applied by the second set of friction brakes increases.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where when
braking the vehicle in the third phase of control, the desired
amount of regenerative braking is decreased preceding the
application of the second set of friction brakes.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where when
braking the vehicle in the first phase of control, no friction
brakes are used.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where the first
value of braking is a maximum output of the regenerative braking
torque.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle where braking
from only the first set of brake and the second set of brakes is
applied if a vehicle speed of the is less than a predetermined
threshold.
In yet another aspect of the present invention, a method is
provided for controlling the braking of the vehicle that has a
first set of friction brakes for applying a first brake apply force
to a first set of wheels coupled to a non-driven axle, a second set
of friction brakes for applying a second brake apply force to a
second set of wheels coupled to a driven axle. A powertrain
assembly is coupled to the driven axle. The powertrain assembly
includes a regenerative braking unit capable of recapturing kinetic
energy from driven axle. The vehicle is braked in a first phase of
control using regenerative braking to brake the driven axle to
achieve up to a first value of braking force. The vehicle is braked
in a second phase of control using the regenerative braking to
maintain braking of the driven axle at the first value of braking
force while selectively applying the first friction brakes to the
first set of wheels of the non-driven axle up to a second value of
braking force. The vehicle is braked in a third phase of control by
selectively applying the first friction brakes to the first set of
wheels and the second friction brakes to the second set of wheels
together with a desired amount of regenerative braking when above
the second value of braking force.
In yet another aspect of the present invention, a method is
provided for determining brake control between a non-driven axle
and a driven axle in a braking system. The braking system includes
an electric motor for applying a regenerative braking force to the
driven axle. The braking system further includes a first set of
friction brakes for applying a first brake apply force to a first
set of wheels coupled to the non-driven axle and a second set of
friction brakes for applying a second brake apply force to a second
set of wheels coupled to the driven axle. A pressure input command
is received relating to a total braking force for braking a
vehicle. A determination is made if an actual regenerative braking
force is greater than the total braking force demand. If the actual
regenerative braking force is greater than the total braking force
demand, then the regenerative braking force is used to brake the
driven axle up to the total braking force demand. If the actual
regenerative braking force is less than the total braking force
demand, then the first brake apply force is determined for applying
to the first set of friction brakes of the non-driven axle and the
second brake apply force is determined for applying to the second
set of friction brakes of the driven axle. The sum of the first
brake apply force and the second brake apply force being equal to
the total braking force demand. A determination is made whether the
second brake apply force is greater than the actual regenerative
braking force. If the actual regenerative braking force is greater
than the second brake apply force, then the actual regenerative
braking force is applied to the driven axle up to the second brake
apply force and applying the first braking force to the first set
of friction brakes of the non-driven axle. If the actual
regenerative braking force is less than the second brake apply
force, then determining the brake apply difference between the
second braking force and the actual regenerative braking force. The
actual regenerative braking force is applied to the driven axle.
The first brake apply force is applied to the first set of friction
brakes of the non-driven axle. The brake apply difference is
applied to the second set of friction brakes of the driven axle, in
response to the regenerative braking is force being less than the
second brake apply force.
In yet another aspect of the present invention, a method is
provided for determining brake control between a non-driven axle
and a driven axle in a braking system where the actual regenerative
braking force applied to the driven axle is applied up to a first
value of braking force.
In yet another aspect of the present invention, a method is
provided for determining brake control between a non-driven axle
and a driven axle in a braking system where the actual regenerative
braking force applied to the driven axle and the first brake apply
force applied to the first set of friction brakes of the non-driven
axle are cooperatively applied up to a second value of braking
force.
In yet another aspect of the present invention, a method is
provided for determining brake control between a non-driven axle
and a driven axle in a braking system where the actual regenerative
braking force applied to the driven axle, and the first brake apply
force applied to the first set of friction brakes of the non-driven
axle, and the brake force difference applied to the second set of
friction brakes of the driven axle are cooperatively applied above
the second value of braking force.
In yet another aspect of the present invention, a method is
provided for determining brake control between a non-driven axle
and a driven axle in a braking system where the actual regenerative
braking force decreases when above the second value of braking.
In yet another aspect of the present invention, a method is
provided for determining brake control between a non-driven axle
and a driven axle in a braking system where braking from only the
first set of friction brakes and the second set of friction brakes
is applied if a vehicle speed is less than a predetermined
threshold.
In yet another aspect of the present invention, a method is
provided for controlling a vehicular regenerative braking system
that includes a first set of friction brakes for applying a first
brake apply force to a first set of wheels coupled to the
non-driven axle. A second set of friction brakes applies a second
brake apply force to a second set of wheels coupled to a driven
axle. A powertrain assembly is coupled to the second set of wheels.
The powertrain assembly includes a regenerative braking unit for
applying a regenerative braking force to the driven axle. A desired
brake balance line representative of a ratio of braking forces
between a first set of brakes of a non-driven axle and a second set
of brakes of a driven axle is determined. The desired brake balance
ratio includes a first, a second, and a third control phase. The
regenerative braking force is applied to the driven axle in the
first control phase up to a first value of brake force. The first
brake apply force and the regenerative braking force are
cooperatively applied in the second control phase up to a second
value where the second value is in a region of front bias braking
balance control. The second brake apply force together with the
first brake apply force and the regenerative braking force are
cooperatively applied in a third phase of control up to a third
value of braking.
In yet another aspect of the present invention, a method is
provided for controlling a vehicular regenerative braking system
where the third value of braking is disposed in the region of the
front bias braking balance control.
In yet another aspect of the present invention, a method is
provided for controlling a vehicular regenerative braking system
where the third value of braking is disposed on the desired brake
balance line.
In yet another aspect of the present invention, a method is
provided for controlling a vehicular regenerative braking system
where the second value of braking is disposed on the desired brake
balance line.
In yet another aspect of the present invention, a method is
provided for controlling a vehicular regenerative braking system
where the second brake apply force is applied in the second control
phase.
In yet another aspect of the present invention, a method is
provided for controlling a vehicular regenerative braking system
where the total of the regenerative braking force, the first brake
apply force, and the second brake apply force is proportional
between the non-driven axle and the second set of wheels of the
driven axle. The ratio of braking forces between the non-driven
axle and the driven axle increases along a line parallel to the
desired brake balance line throughout the second control phase as a
total brake demand increases.
In yet another aspect of the present invention, a method is
provided for controlling a vehicular regenerative braking system
where the regenerative braking force is not applied if a vehicle
speed is less than a predetermined threshold.
The principle and mode of operation of this invention have been
explained and illustrated in its preferred embodiment. While the
embodiments of the invention have been described as used in
conjunction with regenerative braking, it is understood that these
embodiments and variations thereof can also be incorporated in
conventionally fueled vehicles without regenerative braking. It is
further contemplated that the method of control of this invention
may be applied to vehicle having regenerative braking available on
one, two, or more axles and may be applied to vehicles having
regenerative braking on any combination of a rear axle, a group of
rear axles, a front axle, a group of front axles, and one or more
axles between a front and rear axle. Further, it is understood that
this invention may be practiced otherwise than as specifically
explained and illustrated without departing from its spirit or
scope.
TABLE OF REFERENCE NUMBERS
10 vehicle system 11a friction braking system 11b regenerative
braking system 12a, 12b frictional front wheel brakes 13a, 13b
frictional rear wheel brakes 14 powertrain assembly 15 engine 16
transaxle 17, 18 front wheels 19 electric motor 20, 21 rear wheels
22 rear axle 23 front axle 24 energy storage device 25 accelerator
pedal 26 brake module (HCU) 27 electrical control unit (ECU) 28
brake pedal 29 master cylinder 30, 32, 34, 36 Wheel speed sensors
31 first electric motor 33 second electric motor 38 brake pedal
pressure sensor 39 driveshaft 40 battery temperature sensor 42
state of charge sensor 44 first brake circuit 45 ambient
temperature sensor 46 second brake circuit 47 third brake circuit
48 fourth brake circuit 49 PCM 50 ideal brake balance 51 preferred
control algorithm 52 preferred brake blending balance 53 desired
brake balance 54 brake blending balance 57 regenerative braking
portion 58 regenerative and rear braking 59 brake blending balance
60 brake blending balance 61 regenerative braking portion 62
combined braking force portion 63 brake blending balance 64
regenerative braking 65 combined braking force portion 72 P.sub.cmd
73 Act_Torq 74 Regen_Torq_Req 75 Friction_Press 76 Front_Rear_bal
77 Press_Torq 79 switch 80 switch 81 Total 82 Driven_Axle 83
Non_Driven Axle 84 gate 85 gate 90 summation black 91 summation
block
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